According to people familiar with the matter, Apollo Global Management is in talks to raise senior financing for Elon Musk’s proposed acquisition of Twitter Inc. The funding, arranged by Morgan Stanley, will be more than $1 billion and could include firms such as Sixth Street Partners, people familiar with the matter said. Shares of Twitter closed at $47.26 a share on Tuesday as traders doubted Tesla Inc CEO Elon Musk’s close at $54.20.

Musk revealed last week that he had received $ 7.1 billion in equity pledges from investors, including Larry Ellison, Sequoia Capital and Qatar. He persuaded Saudi Prince Alwaleed bin Talal to sell his $1.9 billion Twitter stock to the private company and is seeking to do the same with Twitter co-founder Jack Dorsey.

It’s unclear how the preferred stock will change the existing funding package, which would require Musk and his partners to contribute $27.25 billion in equity to fund the $44 billion acquisition, with the rest from junk-rated debt and a margin loan linked to Tesla’s stock.

Preferred stock is a mix of debt and equity capital and is higher than common stock in the capital structure. Some preferred stock can be converted into common stock at a pre-agreed price. Musk, who recently increased his cash position by selling Tesla stock for about $8.5 billion in the latest round, has amassed 9.6% of Twitter’s outstanding shares.

According to the Bloomberg Billionaires Index, musk is the world’s richest person with a net worth of $231.8 billion, but much of that wealth is illiquid. Tesla shares have fallen 26% since Musk announced his intention to buy Twitter, raising concerns among investors that he may need to sell or pledge a substantial amount of stock to fund the acquisition.